1. Field of the Invention
This invention relates to a page printer in which a light beam controlled with a data signal is applied to a photo-sensitive material to record characters, patterns, etc. on a recording sheet in accordance with the principles of electrophotography.
2. Description of the Related Art
A page printer based on the principle of "xerography" has been developed in order to improve the print quality and printer speed. In that page printer, a light beam controlled with printing data is applied to a photo-sensitive material to form a latent image thereon. The latent image is developed with coloring toner and fixed on a printing sheet.
The page printer of the type described above is shown in FIG. 9 and includes a horizontal housing M made up of two members N and Q so that the member Q is swung upwardly to open the housing. An optical writing unit is built in the member Q, while a photosensitive drum, a developing unit, etc. are in the member N. A sheet conveying path is provided from one side of the housing to the other side, so as to supply a printing sheet from a sheet cassette R provided on the one side of the housing. Thus, the page printer is of the "clamshell" type.
The above-described page printer has a number of deficiencies. For example, since the light beam generating unit and the photo-sensitive drum are positioned relative to one another by means of a hinge mechanism S of the housing M, the positioning of the light beam generating unit and the photo-sensitive drum may be inaccurate. In addition, in order to provide a sheet storage section and a printing route section, the device occupies a floor area at least two times the area of a printing sheet.
In order to overcome the above-described drawbacks, the present applicant proposed a page printer in Japanese Patent Application (UPA) No. 234167/1987 (the term "UPA" as used herein means an "Unexamined Published Application"). In that page printer, the sheet conveying path is substantially vertical, and the light beam generating unit is substantially vertical, and the light beam generating unit and the photo-sensitive drum are provided on the base side.
The page printer thus proposed is advantageous in that the floor area required for installation is decreased, and the positioning of the light beam generating unit and the photo-sensitive drum relative to each other is more accurate. However, it is still disadvantageous in that the maintenance is rather troublesome because the photo-sensitive drum must be mounted or demounted from the side. Furthermore, since a variety of units are arranged vertically, toner scattering from the photo-sensitive drum may stick onto the other units, thus staining the printing sheet.